Physics · KS3 and GCSE · Interactive lesson
Forces, mass, weight and turning effects
Compare pushes and pulls, then explore weight and moments. Begin with balanced forces before trying GCSE force calculations.
Choose your view
Explore an interactive example, then try the questions at your own pace.
KS3 / GCSE · start with the idea
By the end of this lesson: Use the overall force to explain whether motion changes.
The interactive diagram and controls are in Stage 2, “Explore one example”. Read the idea here, then try it next.
- A force is a push or pull. An arrow can represent its strength and direction.
- Equal opposite forces balance. The object’s motion does not change.
- If the forces are unequal, the motion changes towards the larger force.
Useful starting points
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What do the words mean?
- N (newton)
- The unit used to measure force.
- Mass
- Measured in kilograms (kg). More mass means less acceleration for the same resultant force.
- Velocity
- Speed and direction together. Right is positive in this example.
- m/s²
- Each second, the velocity changes by this many metres per second.
Change the example
This is the lesson example. Your practice question uses its own numbers.
Something to try
Make the left and right forces equal. Compare an object at rest with one already moving. Does zero overall force mean zero speed?
Notice what changes
How particle motion works +
Starts paused. Press Play, then add energy to see the warmer particles move faster.
Particles keep the same size. Liquid particles move around; solid particles vibrate around fixed positions. This is a simplified model, with the change in motion exaggerated to make it easier to see.
About the playback +
About this model
This example includes all horizontal forces. We are looking at how motion changes, without calculating acceleration.
More about this diagram
Still picture. Play particle motion in Stage 2.
Resultant force = 4 N to the right.
Still picture of the example from Stage 2. Use the back arrow to change it.
Work through it
Starting example: read the steps below
- Compare the forces: 6 N right and 2 N left.
- Subtract the smaller force from the larger: 6 − 2 = 4 N.
- The resultant force acts to the right. The motion changes in that direction.
- An object moving right speeds up. An object at rest starts moving right.
Try on your own
Your turn. No rush.
Question 1
An object has 8 N to the right and 3 N to the left. What is the resultant force to the right?
About these questions
Questions appear in a mixed order. Work at your own pace and stop whenever you like.
These questions use their own numbers, separate from the lesson example. You can stop whenever you like. Answers last for this visit to the page.
A good place to pause
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Can you find the overall force and explain how it changes motion?
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Notes for parents and tutors
These lessons cover selected KS3 and GCSE ideas for England; they are not a complete course. The level notes explain where GCSE methods or optional extensions begin. Maurice can help you choose material for your course and exam board.
The content draws on the DfE Maths curriculum, DfE Science curriculum and AQA GCSE Physics specification. Level labels are guidance, not exam-board endorsements. For AQA Radioactivity, calculating net decline as a ratio is Higher-tier work. Net means the overall change; ask Maurice whether this extension is relevant to your course. Explanations and practice were reviewed during development on 21 October 2026; Maurice should check their fit before assigning work.
Topic labels and your lesson-view preference are saved in this browser. This tab also remembers the last lesson stage, so you can choose to continue there. If you choose revision, selected activities and suggested revisit dates are saved here too. Recent question codes are also kept to reduce repeats. Reflection notes are saved automatically per topic when you type them; you can delete a note in the recap. They stay in this browser and are visible to other people using it. Practice answers and enquiry details are not saved. Clearing browser data removes the labels.